1. Field of the Invention
The present invention relates to a control apparatus for a hybrid vehicle, and in particular, relates to a control apparatus for a hybrid vehicle that can improve fuel consumption by a cylinder deactivated operation of an engine under certain conditions.
2. Description of the Related Art
Conventionally, hybrid vehicles having an engine and a motor as a drive source for a vehicle are known. One type of such a hybrid vehicles is a parallel hybrid vehicle in which the drive output from the engine is assisted by the motor.
In the parallel hybrid vehicle, at the time of acceleration the driving power output from the engine is assisted by the motor, while at the time of deceleration, various control is carried out such as performing battery charging by deceleration regeneration, so that the remaining charge (electrical energy) of the battery can be increased while satisfying the requirements of the driver. Furthermore, since the structural mechanism is such that the engine and the motor are arranged in series, the structure can be simplified, and the whole system can be reduced to a low weight. Therefore, there is an advantage in that there is a high degree of freedom in vehicle assembly.
In order to eliminate the influence of engine friction (engine braking) at the time of deceleration regeneration, several mechanisms have been proposed for the aforementioned parallel hybrid vehicle, such as a mechanism which includes a clutch between the engine and motor (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2000-97068) or the engine, motor and transmission are connected in series (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2000-125405) in order to achieve maximum simplification.
However, in the former mechanism comprising a clutch between the engine and motor, have drawbacks in that the structure becomes complicated by inserting the clutch and the assembly capability of the vehicle is reduced so that insertion of the clutch reduces transmission efficiency of the power transmission system. On the other hand, in the latter construction in which the engine, motor and transmission are connected in series, since the regeneration energy is reduced by the aforementioned friction of the engine, the electrical energy that could be conserved by regeneration is reduced. Therefore, there is a problem in that the assist amount by the motor is limited.
A measure to reduce the friction loss during deceleration is proposed to control the throttle valve in the opening side in the deceleration mode of the vehicle by employing an electronic controlled throttle mechanism for sharply reducing the pumping losses and for increasing the deceleration regeneration. However, since a large amount of fresh air normally flows into the exhaust system, it reduces the temperature of the catalyst and an A/F (air/fuel) sensor, so that the optimum control of the exhaust gas is degraded.